Slight Risk of Thundery Showers 09Z-20Z Eastern half of Ireland, Central & Northern UK as per map Tues 10th July
Slight Risk of Funnel Cloud Development
Confidence level; Low
A complex outlook with several weak frontal boundaries connected to a stationary surface low over the UK. Long wave upper trough extends to primarily effect Ireland but with only marginal influence across the UK. Upper shear values and PV rather weak for both UK & Ireland.
ATM a rather low end outlook so I will keep the detail brief for now; Both GFS and WRF break out convective showers quite early in the period across central UK regions. Some good potential for insolation by mid day onwards and could well turn some of these thundery. A very moist boundary layer with a good ratio for dew points to surface temps should develop some fairly low cloud bases. Models suggest a hard convergence zone running from just west of the Wash up to western Scotland. Much of the initial convective development will likely trigger along this zone. A higher resolution look at the surface flow looks to develop an optimum confluent vector where strong horizontal shear can develop. This low level vorticity can easily be stretched upward into any passing updraft and hence a risk of funnel clouds. Having said that I do not see the outlook comparable to a classic funnel day; The atmosphere looks saturated up to the tropapause and this will likely reduce buoyancy above the LFC and hence might impede updrafts. It is also noted that any instability across the UK will be tied directly into surface heating. The strongest lapse rates will therefore occur close to the ground whereas we are likely to see relatively weak lapse rates aloft.
This post has been edited by Tony Gilbert: 09 July 2012 - 20:14